Global Concern
The globalization of business, travel and communication brings increased attention to worldwide exchanges between communities and countries, including the potential globalization of the bacterial and pathogenic ecosystem. Bactericides and fungicides have been developed to control diseases in man, animal and plants, and must evolve to remain effective as more and more antibiotic, pesticide and insecticide resistant bacteria and fungi appear around the globe.
Bacterial resistance to antimicrobial agents has also emerged, throughout the world, as one of the major threats to both man and the agrarian lifestyle. Resistance to antibacterial and antifungal agents has emerged as an agricultural issue that requires attention and improvements in the treatment materials in use today.
For example, focusing on plants, there are over 300,000 diseases that afflict plants worldwide, resulting in billions of dollars of annual crop losses. In 1990, over 7.3 billion dollars were spent in the United States on pesticide products.
Antibacterial and antifungal (Anti-B/F) agents include, but are not limited to, metallic copper (Cu), copper salts, copper complexes, metallic zinc (Zn), zinc oxides, zinc salts, metallic silver (Ag), silver salts, silver complexes, titanium dioxide (TiO2), cerium oxides, magnesium oxides, zirconium oxides, polyethyleneimine (PEI), carbon, mixed carbon or soot, fullerenes, carbon nanotubes and the like. The preceding compounds are only a few examples of antibacterial and antifungal agents used by man in a quest to control or eliminate infectious diseases in our global environment.
The antibacterial/antifungal (Anti-B/F) formulations in existence today could be improved and made more effective if the following features were included in the formulation. For example, a desirable formulation would have an increased, uniform distribution on a treated surface area, improved adherence to treated surface, a means for controlling and sustaining the release of the active ingredients, and dosage levels that avoid any toxic impact on the environment and/or the treated surface.
The present invention provides a composition that hosts antibacterial/antifungal formulations and together, the host composition and antibacterial/antifungal ingredients provide functional benefits that solve many problems and overcome many limitations in the prior art.
A synthesis method for preparation of a silica matrix with embedded metallic particles is reported in U.S. Pat. No. 6,548,264 to Tan et al., U.S. Pat. No. 6,924,116 to Tan et al., and U.S. Pat. No. 7,332,351 to Tan et al., which are incorporated herein by reference.
Use of Copper (Cu) Fungicides/Bactericides
In modern agriculture, copper (Cu) compounds are widely used as fungicides/bactericides. Cu compounds, in relatively low concentration, are quite toxic to thalophyte organisms, such as, fungi, bacteria, and algae. This property of toxicity has been utilized for over 100 years for control of fungal and bacterial diseases of plants. In 1761, it was discovered that seed grains soaked in a weak solution of Cu sulfate inhibited seed-borne fungi.
The greatest breakthrough for Cu salts undoubtedly came when the French scientist Millardet announced to the world in 1885 that he had found a cure for the dreaded mildew using mixtures of Cu sulfate, lime and water (known as Bordeaux mixture). Cu based fungicides/bactericides are used worldwide because Cu compounds are relatively safe; development of resistance by plant pathogens has been minimal; in demand by developing third world countries and the increasing requirements for food requiring more efficient agriculture; and an increase in government regulations and restrictions or outright banning of alternative products due to their toxicological and environmental impact requires safe treatment formulations, as discussed by H. W. Richardson in Handbook of Copper Compounds and Applications, “Copper fungicides/bactericides” H. W. Richardson, Editor, 1997, Marcel Dekker, Inc.: New York, N.Y., pages 93-122.
The toxicity of Cu is largely due to its tendency to alternate between its cuprous, Cu(I), and cupric, Cu(II), oxidation states. Under aerobic conditions, this redox cycling leads to the generation of highly reactive hydroxyl radicals that readily and efficiently damage biomolecules, such as DNA, proteins, and lipids. The underlying Fenton-like reactions involving reactive oxygen species can be described as Cu-catalyzed Haber-Weiss reactions. While the reaction of dihydrogen peroxide with superoxide primarily has a negligible rate constant as shown below in equation 1, this rate is greatly accelerated in the presence of Cu.H2O2+O2−→O2+OH−+OH*  (1)Cu ions are believed to catalyze this reaction as shown in equations 2 and 3.Cu(II) is initially reduced by superoxide as shown in equation 2,Cu(II)+O2−→Cu(I)+O2  (2)followed by reoxidation by dihydrogen peroxide as shown in equation 3,Cu(I)+H2O2→Cu(II)+O2+OH−+OH*  (3)resulting in a net production of the hydroxyl radical.
Most fungicides and bactericides do little to kill an established infection of fungi and bacteria, respectively, but act by protecting the host from the possibility of infection. If the protectant is applied after the onset of disease symptoms, control will often be minimal. Similarly, Cu compounds inhibit germination of the fungal spore or bacterial cell, the primary “seeds” responsible for dissemination and reproduction of the fungus or bacterium. Because the spore or cell removed from the current infection cycle does not mature nor reproduce in the presence of Cu, the fungus or bacterium are effectively killed.
The fungicidal/bactericidal value is a measure of the toxicity of a material to the pathogen and is usually expressed as an LD50, primarily a laboratory based in vitro toxicity measurement, wherein LD stands for Lethal Dose and LD50 is the amount of material or dose which causes the death of 50% of the target population.
The protective value is a measure of the ability of a material to protect the host organism, for example, a plant, from infection, which is primarily a measurement under field conditions. For example, Cu sulfate has an excellent ability to inhibit fungal spore or bacterial cell germination in the laboratory; however, in the field it exhibits no persistence, because of its solubility. It has limited protective value because it is quickly removed from the plant surface at the first rain. Furthermore, Cu sulfate may produce sufficient soluble Cu to be toxic to the plant (phytotoxic). A Cu compound must be chosen that is relatively resistant to weathering and supplies enough Cu to be toxic to the fungal spores and bacterial cells without adversely affecting the plant.
An important consideration is whether to use “soluble” or “insoluble” copper (Cu) for long-term fungicidal or bactericidal protection. The “soluble” Cu refers to Cu based salts (such as Cu sulfate) that hydrolyze completely in water, producing ionic Cu. The “insoluble” (sparingly soluble) Cu compounds act as a reservoir from which Cu ion is released to the plant surface on which it is deposited upon application.
Solubilization of Cu in the field application is governed by several interrelated factors, such as, the total soluble Cu that is dependent on gross factors such as dosage/residue and the amount at any locus is dependent on distribution. In addition, the limiting concentration of soluble Cu will be dictated by the thermodynamic tendencies of the Cu compound to solubilize in the surrounding media and the concentration of soluble Cu at any given time will be further dependent on the rates at which solubilization occurs, for example, the velocity response of the system toward equilibrium. All of these factors are complicated by the system dynamics. The total dosage/residue decreases over time due to weathering and redistribution of the remaining residue occurs. Particles are exposed to constantly varying moisture and exudate levels, and the system is constantly in a state of flux, moving toward equilibrium. Therefore, the system must be kinetically responsive if toxic doses of Cu are to be maintained. For long-term protection, “insoluble” Cu appears to be preferred in field applications.
Thus, certain properties must be optimized if copper (Cu) fungicides/bactericides are to demonstrate effective protective ability. A dosage must be chosen which is adequate to defend against infection. The deposition of the Cu particles on the plant surface must occur and they must adhere to and/or be retained by the surface. The properties of the adherence by the Cu particle and the retention by the plant surface are determining factors of the tenacity, or overall ability of the Cu compound to persist on the plant surface. Factors such as wind, rain, and leaf movements will all cause erosion of the Cu particle deposits by physical and mechanical means. Rain, mist, and dew will also give rise to the chemical dissolution of those deposits. All of these factors are important in the establishment and maintenance of sufficient coverage to protect plants from pathogens.
The limiting quantity and nature of soluble Cu species at equilibrium with the surrounding media is governed by the absolute solubility of the Cu compound in water and the nature and concentration of the complexing agents present in the media. The quantity of dissolved Cu at any given time is also determined by the rate at which the equilibrium can be established. Equilibrium conditions are determined by the system thermodynamics. The rate at which equilibrium is established is dictated by the kinetic responsiveness of the system. It should be emphasized that thermodynamic considerations allow the identification of the position of the system relative to equilibrium. Further, there will be a tendency to move toward the equilibrium. Understanding of these factors is crucial for developing a new generation of Cu based fungicides/bactericides with sustained ionic Cu release mechanism.
Estimation of the world market for fungicides and bactericides by type of Cu compound and year of introduction is shown in Table 1 below (data published in 1988, Source: H. W. Richardson, Handbook of Copper Compounds and Applications, supra).
TABLE 1Estimation of World Market for Fungicides/Bactericides by Type of Cu CompoundQuantity% ofYearCu Compound(Tons/Yr)MarketIntroducedCu(II) oxychloride71,00051.11990Cu(II) sulfate48,00034.61761Cu(II) sulfate + lime 1873(Bordeaux mixture)Cu(II) sulfate + soda ash (Burgundy mixture)Basic Cu(II) sulfateCu(I) oxide6,0004.31932Cu(II) hydroxide11,0007.91960Others: Cu(II)ammonia complex., 1917CO3 and PO4It is clear that Cu based fungicides/bactericides have been applied for a long-time and have high societal and economic impact in agriculture, water treatment and domestic living. There are approximately 2,000 registered products which contain copper compounds as active ingredients.
Several Cu compounds are registered in the United States for management of over 100 diseases on almost 50 food crops. The Cu compounds exhibit varying degrees of effectiveness for any target organism on any given host. The most common forms of Cu that satisfy these conditions to varying degrees are the normal hydrolysis products of Cu(I) and Cu(II) salts (also known as “insoluble Cu” of “fixed Cu” compounds): Cu(I) oxide (Cu2O), Cu(II) oxychloride (CuCl2.3Cu(OH)2), tribasic Cu(II) sulfate (CuSO4.3Cu(OH)2, and Cu hydroxide (Cu(OH)2). In the past most Cu products were wettable powders and contained around 50% Cu (active ingredient). However today's formulations contain from 8% to 75% Cu and application rates varying accordingly. Products are formulated as wettable powders, wettable granules, liquid flowable suspensions and aqueous liquids.
By the mid-1930s, Bordeaux mixture was largely replaced by basic Cu(II) sulfate, Cu(I) oxide, Cu(II) oxychloride. These Cu compounds are easy to handle and relatively less phytotoxic in comparison to the Bordeaux mixture. Cu hydroxide was introduced in 1960. Kocide® 3000 is the latest Cu hydroxide based product from the DuPont Company, Wilmington, Del., which is one of the most popular fungicides/bactericides.
Currently used Cu compounds possess unique set of physical and chemical properties. They differ in their total amount of metallic Cu content and aqueous solubility. It is well understood that the antibacterial activity will depend upon the availability of soluble (“free and reactive”) Cu ions in the formulation. Among the existing Cu compounds, tribasic Cu sulphates and cuprous oxide are least soluble, whereas Cu hydroxides are more soluble than Cu oxychloride.
Again, too much Cu will cause phytotoxicity and adversely affect the environment whereas sparingly soluble Cu compounds will be less effective, requiring multiple applications, thus labor extensive. A robust Cu formulation must meet at least the following three criteria: (i) the Cu release rate must be maintained at a optimum level (sustained release mechanism while minimizing phytotoxicity) to provide long-term protection against pathogen, (ii) the Cu compound must stick well to the plant surface to withstand wind blown rain so that multiple applications will not be required and (iii) the Cu compound will not cause toxicity to the environment (i.e. environmentally-safe). Due to inherent chemical and physical properties, however, the existing Cu compounds are seriously limited to meet these criteria.
With regard to copper (Cu) compounds, the efficacy of a Cu compounds can be considerably improved by reducing the particle size according to Torgeson, D. C., ed. Fungicides—An Advanced Treatise, Agricultural and Industrial Applications and Environmental Interaction. Vol. 1. (1967), Academic Press: New York, N.Y., page 697. The smaller the particle size the greater is the number of particles per gram and therefore the greater the fungicidal or bacterial activity. This welcomes nanoscience and nanotechnology that deals with matters in the nanoscale dimension, typically 1-100 nanometer range.
Navarro, E., et al., in “Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi,” Ecotoxicology, 2008. 17(5): pages 372-386 teaches that specific surface area as shown in FIG. 1a increases exponentially as the particle size decreases below 100 nanometers. Likewise, Oberdorster, G. et al, in Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles, Environmental Health Perspectives, 2005. 113(7): pages 823-839 teaches that the percentage of surface atoms exponentially increase as the particle size decreases below 100 nm as shown in FIG. 1b. Thus, with smaller particles coverage is improved and there is significantly more surface area available per gram of product to release Cu ions when moisture is present.
Smaller particles also resist dislodgement better as they are lighter and have a larger surface area relative to their weight; hence a greater area of contact with the plant surface, and the result is an increase in the total force of adhesion. Cu formulations with smaller particles will therefore produce improvements in disease control through better coverage, rain-fastness, and longevity of the product and release of Cu ions on the plant surface. In this regard, some improvements in the product quality have been made on Cu compounds over the past decade. To date, however, no major breakthrough has been made that could be considered revolutionary. This strongly demands development of a new generation of Cu based fungicides/bactericides that will meet the above-mentioned criteria.
Inhibiting Growth of Mold and Mildew
Growth of fungus, such as, mold and mildew fungi is a serious problem in warm, moist environments, such as in tropical climates. In the presence of nutrients which are found abundantly in house/building materials such as dry walls, wood, grout, carpet backing and the like, mold and mildew thrives.
Mold and mildew have similar characteristics, but are different types of microscopic fungi and are often different in color and texture and can be seen growing on objects both inside and outside buildings. Mold and mildew growth is not only detrimental to health but also presents an unsightly appearance when colonies are established on interior or exterior surfaces of buildings. Mildew is more often found in bathroom showers, tubs, ceramic tile grout, paper and fabric; mold is usually found in foods. They can be difficult to tell apart as they both use spores for reproduction. Mold is often black, green, red or blue in color, while mildew is usually gray or white. Musty and moldy odors are produced by chemical changes taking place during the mold life process and are scientifically designated as microbial Volatile Organic Compounds (mVOCs) Waste products are given off by actively growing molds.
Airborne mold spores can seriously compromise indoor air quality and cause severe allergy, asthma and other immunological problems. Health effects such as headaches, dizziness, nausea and coughing have been linked to exposure to mVOCs. Irritation of the eyes and throat may also occur as a result of breathing mold toxins. Moldy food should not be eaten. A mildew infestation on paper and some fabrics cannot be scrubbed off, but a mildew remover can usually get rid of mildew on harder surfaces, such as, surfaces in bathrooms, kitchens and on exterior walls.
Mold spores are resistant to high temperature, UV light and desiccation. The spores are abundant in the environment and remain dormant in unfavorable conditions and germinate rapidly in a favorable environment (warmth, moisture and nutrients). Bleach solutions are effective in killing both mold and mildew and are considered a very effective treatment world-wide. However, the action of bleach does not last long; multiple applications are required within one or two weeks.
U.S. Pat. No. 3,992,146 to Fazzalari describes a process using biocidal solutions containing copper sulfate and a surfactant to inhibit growth of fungi on hard porous surfaces, such as grout.
It is desirable to use nanotechnology to expand the use of copper (Cu) loaded silica nanoparticle/nanogel formulations with superior antibacterial activity for treating areas that favor and foster the growth of mold and mildew; in addition, it is desirable for a single treatment to remain effective for from at least two to six months because of the release of ionic Cu in a slow, sustained manner and in quantities that would not violate the EPA Water Quality Standard Rule issued on Dec. 1, 1992, setting water quality standards for copper as a priority toxic pollutant.
Treatment of Diseases in Plants
The state of the art for methods and treatment of diseases in plants, and specifically canker in citrus plants is found in a representative sample of patents listed below:
U.S. Pat. No. 3,983,214 to Misato et al teaches fungicidal compositions and method for protecting plants by the use of compositions which contain organic acids as an active ingredient, alkali metal salts of these organic acids, ferric citrate, ferric lactate, glycerine, aluminum chloride and esters formed between sugar and higher fatty acids having 8 to 18 carbon atoms. The compositions have no phytotoxicity and no mammalian toxicity and present no risk of pollution of soil.
U.S. Pat. No. 5,462,738 to LeFiles et al. discloses a granular copper hydroxide dry flowable bactericide/fungicide with improved biological activity and a method of making and using.
U.S. Pat. No. 5,939,357 to Jones et al. provides a fungicide composition which has a bicarbonate-containing inorganic salt ingredient which enhances the efficacy of a fungicide ingredient for treatment of cultivated crops.
U.S. Pat. No. 6,471,976 to Taylor et al. discloses an improved copper complex bactericide/fungicide containing a partially neutralized polycarboxylic acid and a method of making and using.
U.S. Pat. No. 7,163,709 to Cook et al. discloses a composition and method of providing ionic forms or compounds of any combination of three metals (copper, gold and silver) to produce a product that can be used as an antimicrobial agent, hard surface disinfectant, foliar spray or water treatment. The composition is aerosolized, misted, vaporized, fogged, humidified to produce micronized particles which are able to remain in suspension in the air for long periods of time to act on air-borne fungal spores and/or pathogens. This would be an enormously expensive composition.
U.S. Pat. No. 7,226,610 to Winniczuk teaches compositions and methods for the treatment and prevention of disease in plants, especially citrus canker, using composition including various combinations of d-limonene, wax and monohydric alcohol.
U.S. Patent Publ. No. U.S. 2001/0051174 to Staats provides an antimicrobial composition containing quaternary ammonium compounds, a surfactant, a wetting agent, a drying agent, a hydrophilic film forming agent, a hydrophobic water proofing agent and water, having antiviral, antibacterial, and antifungal properties, applied to plants and trees by spray coating and/or through systemic delivery to protect against harmful and destructive organisms.
U.S. Patent Publ. No. US 2007/0087023 and U.S. Patent Publ. No. US 2007/0098806 both to Ismail et al disclose a polymer-based antimicrobial agent that includes a water-soluble polymer and oligodynamic metal ions (e.g., nano-sized silver particles) that interact with the water-soluble polymer to treat or prevent citrus canker.
Thus, there is a wide array of fungicidal/bactericidal compositions represented in the patent literature with formulations that include, acids, polymeric compounds, metallic ions, undesirable components such as surfactants or oils. Cost, effectiveness and bacterial or fungal resistance to treatment are also considerations.
With regard to citrus canker, a particularly acute and critical situation has developed in the United States. Citrus canker is a bacterial disease of citrus that causes premature leaf and fruit drop. Symptoms of the disease are exhibited on leaves and fruit by brown, raised lesions surrounded by an oily, water-soaked margin and a yellow ring or halo. Old lesions in leaves may fall out, creating a shot-hole effect.
Citrus canker does not harm humans or animals or plant life other than citrus. However, citrus canker affects all types of citrus, including oranges, sour oranges, grapefruit, tangerines, lemons and limes. Canker causes the citrus tree to continually decline in health and fruit production. Ultimately, the tree will produce no fruit at all.
Citrus canker is highly contagious and can be spread rapidly by windborne rain, lawnmowers and other landscaping equipment, people carrying the infection on their hands, clothing, or equipment, moving infected or exposed plants or plant parts.
The United States Department of Agriculture (USDA) withdrew eradication program funding due to the impacts of legal constraints and the 2004/2005 hurricanes that caused canker to spread so far that eradication was no longer possible.
Florida is currently under a statewide quarantine by the USDA and no citrus may leave the state unless the USDA has issued a limited permit. No Florida grown citrus may enter any citrus producing states or territories. No citrus plants or parts may enter or exit Florida.
Over 16 million trees have been destroyed in Florida since canker was first identified in Florida in 1910. Twice the state of Florida has declared that canker was eradicated, in 1933 and again in 1994, only to have the canker disease resurface a third-time in 1995 near Miami International Airport. In 2008, the citrus industry in Florida is now quarantined because of canker disease that was spread by the 2004/2005 hurricanes. Once productive groves, land and trees are becoming unproductive at an enormous cost to the state and its citizens.
There remains a continuing need for the development of new and more effective fungicides/bactericides that are inexpensive and easy to manufacture which possess preventive, curative and systemic activity for the protection of not only citrus trees, but all cultivated plants, with a minimum of phytotoxic side effects. The present invention uses nanotechnology to meet the need for an inexpensive, more effective fungicide/bactericide.